(1) Field of the Invention
This invention generally relates to tape guiding devices, especially those used in magnetic tape drive systems. More particularly this invention is concerned with guide devices for restoring and removing tape leader blocks to and from a tape cassette's leader block housing.
(2) Description of the Prior Art
Various devices have been developed for automatically threading magnetic tapes from tape supply reels, past transducer heads, and on to take-up reels. One widely used tape threading device is disclosed in U.S. Pat. No. 4,399,936 ("the -936 patent"). The tape is usually dispensed from a cassette by a pulling action upon a leader block. This action pulls the leader block out of a receiver opening in the cassette's leader block housing. This in turn pulls the tape out of the cassette. The leader block is restored back into the cassette's leader block housing by a pushing action upon the leader block by a threader arm which is coupled to the leader block.
Most leader blocks are housed in a leader block housing which has a diagonal orientation with respect to one corner of an otherwise rectangular-shaped tape cassette. U.S. Pat. No. 4,383,660 ("the -660 patent") well represents this type of tape cassette system wherein the receiver opening presents a diagonal receiver opening in one corner of the cassette. The leader block fills and closes the diagonal opening when the leader block occupies the leader block housing. The leader block is held in the leader block housing by means of a cantilevered arm which forms a part of the front surface of the tape cassette. The cantilevered arm usually has a rounded edge which engages a rounded lip boss on the underside of the front of the leader block. This engagement is in the nature of a compression fit between the rounded edge of the cantilevered arm and a rounded lip boss of the leader block. In effect, the cantilevered arm acts as a projecting leaf spring which positions the leader block within the cassette housing. As is well illustrated in FIGS. 3a, 3b and 3c of the -660 patent, a pushing force upon the leader block will engage and seat it in the leader block housing. In effect, the rounded edge of the cantilevered arm will be pushed slightly downward by a force transmitted to the leader block's lip boss. This force is provided by the forward push of the threader pin under a powered action of the incoming threader arm. Assuming proper alignment between the incoming leader block and the diagonal receiver opening, the rounded lip boss of the leader block will slide past the rounded edge of the cantilevered arm and thereby seat the leader block in the leader block housing.
However, restoration of the leader block to the cassette's leader block housing presupposes that the leader block has been precisely delivered to the receiver opening of the leader block housing. This precise delivery in turn depends on a number of factors including (1) an initial successful coupling of the threader pin with the threader pin receiver in the leader block (2) a continued tight registry between the threader pin and those slots of the leader block which cooperate with the threader pin and (3) lack of wear in other parts of the threader arm system. Therefore, some understanding of certain problems encountered in the restoration and/or removal of leader blocks to and from the cassette's leader block housing also will provide a further appreciation of the utility and advantages of the guide device disclosed in this patent application.
It should first be noted that threader pins which carry leader blocks can have various configurations. For example, they are often presented in the form of a cylinder suspended from a rod which in turn is suspended from a threader pin carrier. The forward ends of the most commonly used leader blocks are usually provided with seating means which are usually presented in the form of openings or slots which are highly registrable with whatever threader pin configuration employed. Most threader pins are intended to complete registry with the leader block's receiver slot while the threader pin is carrying the leader block. Most threader pins currently in use have a relatively short enlarged cylindrical end member whose diameter is greater than that of a more elongated rod-like top portion of the threader pin which in turn is attached to the underside of the threader arm. Preferably, the leader block will be supported in a substantially horizontal orientation by the vertical threader pin when the cylinder of the threader pin is properly seated in, and otherwise in registry with, the threader pin receiver opening in the front end of the leader block.
Threader pin carrier devices such as the one disclosed in the -936 patent deliver their associated threader pin directly to the leader block under the power and action of gear motor torque which is delivered to the threader arm which supports the threader pin carrier. That is to say, the threader arm's gear motor torque is employed both to thread the tape through the tape deck system and to restore and remove the leader block to and from the cassette's leader block housing. Other threader arm devices such as the one described in U.S. patent application Ser. No. 872,951 deliver the leader block to the cassette by means of a gear and motor system which is separate from that of the threader arm. In either case however, the leader block restoration and removal operations cause a great deal of wear upon the openings in the leader block in which the rod and cylinder members of the threader pin are seated. The threader pin itself is also subject to some degree of wear. Moreover, and regardless of whether the threader arm motor is used to directly insert the leader block in the cassette or whether a leader block inserter toggle system is employed for this purpose, the gear/motor systems are themselves subject to varying degrees of wear. The other threading operations that these prior threader arm devices are called upon to perform also produce a great deal of gear/motor wear. Furthermore, the leader block may not be aligned or assembled on the tape itself.
Eventually, wear from all such sources leads to deviations from the preferred horizontal orientation of the leader block with respect to the threader pin from which the leader block is suspended. The end result of such wear is that the rear end of the leader block "sags" downwardly from its preferred horizontal orientation. This sag causes the leader block to collide with the upper and lower edges of the receiver opening of the tape cassette housing. In other words, a collision free insertion of the leader block into the receiver opening of the leader block housing requires that the leader block be in a substantially horizontal orientation. The need for a smooth insertion of the leader block in general, and the rear end of the leader block in particular, are made more pronounced by the fact that delivery of the leader block to the receiver opening of the cassette's leader block housing represents the final phase of a powered delivery of the leader block to the cassette. Moreover, in some prior art devices this powered delivery is carried out at high speeds. Hence, there is a great need to carry out this final phase of the leader block delivery with a high degree of precision. Any substantial misalignment between the incoming leader block and the cassette's receiver opening will cause the leader block to collide with edges of the receiver opening. Hence, wear and particularly wear upon the threader pin seating upon which the cylinder portion of the threader pin rests, is perhaps the largest single factor in producing violent and debilitating collisions between the leader block and the edge of the receiver opening rather than smooth, well aimed insertions of the leader block into the receiver opening.
Slower insertion speeds are not however a particularly viable solution to this collision problem. Both threader arm powered systems and separately powered leader block insertion systems have their own power and/or speed requirements. Consequently, most prior art threader arms are usually designed and powered much more by considerations associated with pulling the tape though a convoluted tape deck path than they are by considerations associated with some eventual collision of the leader block upon some appropriate part of the cassette. Hence there is a need for a device which can quickly and accurately restore a sagging leader block back to a horizontal orientation just prior to its insertion into the receiver opening of the cassette's leader block housing.